Preliminary studies in our laboratory have demonstrated limulus gelation test activity in the plasma of patients with either germ negative infections or prominent gastrointestinal disturbances. In order to study these phenomena further, we will develop two radioimmunoassays: a) for lipid A, the toxic moiety of the endotoxin molecule: b) for Bacteroides Vulgatus surface antigen, a marker for intestinal endotoxemia. Plasma samples stored from the preliminary studies will be retested with the radioimmunoassays to confirm the validity of the original limulus test results. Clinically ill newborns will then be studied prospectively to describe relationships between endotoxemia, depletion of circulating neutrophils and complement, and clinical status. Total hemolytic complement will be measured; levels of complement components Clq, factor B, and C3 will be quantitated by electroimmunoassay. Clinical parameters will be recorded according to a prepared protocol. The study will measure the correlation of endotoxin levels with certain proposed toxic effects of endotoxin, including lethality, evidence of shock, thermal instability, and consumption coagulopathy. We will determine the extent to which neutropenia and complement depletion are involved in these processes.